Method and device for setting the vehicle longitudinal velocity to a deired speed

ABSTRACT

A method and a device for setting the longitudinal speed of a vehicle to a setpoint speed is described, in particular on the basis of a regulation, having controllable brake units. In operation of a cruise control system, it may occur that the cruise control is activated again when the instantaneous driving speed is significantly higher than the stored setpoint speed. In this situation, there may be unwanted braking responses by the regulator which could endanger the driver and the following road users. In such a situation, the method according to the present invention prevents a braking measure from being implemented and ensures that the vehicle will coast, being braked only by the road resistance and the drag on the engine, until reaching the set speed. Through this method, the driving response of the cruise control system approximates that of a human driver, so the responses of the automatic cruise control seem more intelligible for the driver.

BACKGROUND INFORMATION

[0001] A method and a device for setting the longitudinal speed of avehicle to a setpoint speed are proposed, in particular on the basis ofa regulation, having controllable brake units.

[0002] The basic functioning of such a method and such a device forregulating the speed or acceleration has long been known by the termadaptive cruise control (ACC). A basic description of such a device andsuch a method can be found, for example, in the article “Adaptive CruiseControls —System Aspects and Development Trends” by Winner, Witte etal., published at SAE 96, Feb. 26-29, 1996 in Detroit (SAE paper no.961010).

[0003] Such a method and the respective device are described, forexample, in German Patent Application 196 27 727 A1, where resumingregulation at the original setpoint speed is delayed by the driver in atleast one operating mode. If, when regulation is resumed, the vehiclespeed is greater than the stored setpoint speed, then due to the timelag in resumption the driver has an opportunity to adjust the setpointspeed to prevent an unwanted braking response.

[0004] German Patent Application 42 38 399 A1 describes a method and adevice which work together in the sense of regulating or limitingdriving speed. In this method, an estimate is made to determine whethera reduction in engine power will be sufficient to maintain a setpointspeed. If closing the throttle valve is not sufficient to decelerate thevehicle so that the setpoint speed is maintained, then optionally thebraking power may be increased. This method is used to maintain drivingspeed at a setpoint speed without having to operate the brakes by thebrake pedal.

OBJECT, ACHIEVEMENT AND ADVANTAGES OF THE INVENTION

[0005] With the known cruise control systems, in most cases only thethrottle valve is controlled to regulate the actual speed of the vehicleat a setpoint speed. In isolated cases, there are also known cruisecontrol systems which can control the brake systems as well and can thusmaintain a constant speed even in downhill driving.

[0006] In vehicles with adaptive cruise control, both the throttle valveand the brake may be controlled, depending on the given situation. In anACC system, this is done as a function of the speed or the distance fromthe vehicle in front, depending on whether the vehicle is in distancecontrol mode or speed control mode. In the case when the vehicle is inspeed control mode, i.e., no vehicle is within the sensor sight range infront, the setpoint speed is the same as the set speed selectable by thedriver. In the case when the vehicle is in distance control mode, i.e.,one's own vehicle is following a vehicle in front, the driving speedapproaches the setpoint speed. Therefore, in these ACC systems, brakingis always performed automatically when the longitudinal speed of thevehicle is greater than the set speed. Now there are situations in whichthese regulating responses in the form of braking measures areundesirable and would frighten and even endanger both the driver and thefollowing traffic.

[0007] This situation occurs in particular when the vehicle speed issignificantly higher than the stored set speed, and the driver operatesthe resume button to reactivate the cruise control. Another situation inwhich this response can occur is when the driver steps on the gas pedalwhile ACC regulation is active and thus accelerates the vehicle to asignificantly higher speed than the set speed. At the moment when thedriver lets off the gas pedal again and the vehicle speed is still farabove the set speed, the ACC regulation resumes and the vehicle isbraked to the set speed, although the driver is not expecting thisresponse.

[0008] The present invention should conform with the driving response ofa skillful and experienced driver, so that in the situations describedhere, the system will respond differently than in normal operation. Thegoal is to omit the control of brake units as long as there is notermination criterion such as an obstacle detected in the predicted pathrange of the regulated vehicle or a time limit being exceeded, inparticular in the special cases of resumption of cruise control anddriver override in the case when the vehicle speed is higher than theset speed.

[0009] Through the method according to the present invention and therespective device according to the present invention, the response of anatural driver in these special situations is simulated, thus avoidingunexpected and unnecessary braking maneuvers which could frighten andendanger road users.

DRAWING AND DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0010] Embodiments of the present invention are described below on thebasis of four drawings.

[0011]FIG. 1 shows a v-t diagram in which the longitudinal speed of thevehicle is plotted as a function of time for the case when cruisecontrol is resumed by activating the resume-delay function.

[0012]FIG. 2 shows a v-t diagram in which the longitudinal speed of thevehicle is plotted as a function of time for the case of driver override(suspend) by operation of the gas pedal and subsequent deceleration byreleasing the gas pedal, thus activating the suspend-delay function.

[0013]FIG. 3 shows a block diagram indicating which conditions andstates lead to the resume-delay and suspend-delay operating modes andhow they are terminated.

[0014]FIG. 1 shows a speed axis 102 plotted over a time axis 101, thusforming a v-t diagram. Curve 105 shows vehicle longitudinal speed vFzgas a function of time; this is the speed of the vehicle at time t. Curve107 shows set speed vSet of the adaptive cruise control over time t. Thetime axis is represented by line 101. Line 103 represents the time whenresumption of cruise control is activated by the driver. FIG. 1 showsthat before time 103, vehicle speed vFzg 105 is significantly higherthan set speed vSet 104. At time 103, resumption of control is activatedso the regulation intervenes in the driving process again. Since vehiclespeed vFzg is much higher than set speed vSet 107, in the traditionalcase the regulator operates the brake to set the vehicle to set speedvSet, which thus results in a speed profile such as that represented bybroken line 106. In such a situation, a human driver would allow thevehicle to coast until reaching set speed vSet instead of braking todecelerate. To simulate this behavior, braking is suppressed, resultingin a speed profile such as that represented by curve 105.

[0015] The time curve of the resume-delay flag is plotted in the lowerportion of this diagram. Line 108 shows the times at which theresume-delay flag has been set. In this case, axis 101 is again used asthe time axis.

[0016] The flag is set at the moment when vehicle longitudinal speedvFzg is significantly greater than set speed vSet and the resumption isactivated, preferably by depressing the “resume” key. In this mode, abraking measure is prevented as long as there is no need for it. If asensor detects an obstacle in the vehicle's lane, then it is appropriateto remove the “resume-delay” flag and allow a braking measure. It isalso appropriate to delete the “resume-delay” flag when set speed vSetis changed, preferably when it is reduced or when the “resume-delay”mode lasts longer than a maximum preselectable value. In the normal casethe “resume-delay” flag should be withdrawn only if vehicle longitudinalspeed vFzg is less than a preselectable extent above set speed vSet.This time has been plotted in FIG. 1 in line 104 at which “resume-delay”flag 108 is also withdrawn.

[0017] Another situation in which it is appropriate to prevent a brakingmeasure is when the cruise control is overridden by stepping on the gaspedal and the longitudinal speed of the vehicle is increasedsignificantly in comparison with set speed vSet. This case is describedbelow as a “suspend-delay” function and is illustrated in FIG. 2. FIG.2, like FIG. 1, shows a v-t diagram. The speed axis is 202 and the timeaxis is 201. Curve 208 represents vehicle longitudinal speed vFzg as afunction of time t; 207 is set speed vSet of the cruise control.

[0018] Before time 203, vehicle speed vFzg fluctuates around set speedvSet. At time 203, the gas pedal is operated in the sense of increasingthe vehicle speed, so that vehicle speed vFzg is increased significantlyin comparison with set speed vSet. The gas pedal remains in operation attime 206, so the vehicle's speed is increased further in this period oftime. At time 205 the gas pedal returns to its original position. Intraditional operation, the regulation intervenes again, reducing thespeed to set speed vSet by a breaking measure, as illustrated by curve211. Due to the fact that braking is prevented in this situationaccording to the present invention, the vehicle is braked only by theroad resistance and the drag of the engine, so the speed curve drops asin 208, so it declines much more slowly than in the case of curve 211.

[0019] At time 205, vehicle speed vFzg has decreased to the extent thatvehicle longitudinal speed vFzg is less than a preselectable extentabove set speed vSet. As in the “resume-delay” case, this is also one ofthe termination criteria for the “suspend-delay” case. Other terminationcriteria include exceeding a time limit for this operating mode,detecting an obstacle in the same lane as the vehicle, a reduction inset speed by operation of an operating element or deactivation of thedistance and speed regulation system.

[0020]FIG. 2 shows in the lower portion two curves 209 and 210 whichcorrespond to the time axis and the v-t diagram. 209 is the“suspend-delay” flag which is set at time 204 when the regulatorintervenes in the speed control again under the condition that thevehicle longitudinal speed is much greater than the set speed. As longas this “suspend-delay” flag is set, braking is prevented until time 205when this flag is reset because the vehicle speed is no longersufficiently higher than the set speed. Line 210 shows in which periodsof time the gas pedal is operated in the sense of a desiredacceleration. The gas pedal is operated at time 203 in the sense ofincreasing speed, it remains activated for time period 206, and it isreturned to the starting position at time 204.

[0021] For the case when one of these two operating modes —“resumedelay”or “suspend-delay”— is active when driving downhill, a braking measureis provided but it is only as great as required by the gradient so asnot to further accelerate the vehicle.

[0022]FIG. 3 illustrates the states and transitions such as thoseoccurring with the “resume-delay” and “suspend-delay” modes and howthese modes can be canceled again. For example, region 301 describes anactive cruise control system, in contrast with block 302, which showsthe operating mode when the cruise control, which may also be anadaptive cruise control (ACC), has been deactivated. Block 303 withinmode 301 represents the normal operating case of the cruise control,also referred to as the first operating mode in the main claim.Transition 308 from the shutdown state to the active normal operatingmode represents activation by an operating element. Conversely,transition 309 represents deactivation of the cruise control byactuating a shutdown operating element.

[0023] Two possible modes can be assumed from mode 303. One is mode 304,which can be reached transition 310. Transition 310 occurs when thebrake pedal has been actuated by the driver, whereupon the cruisecontrol system is deactivated and goes into the “resume” mode. If theoperating element for resuming cruise control is actuated in this mode,under the assumption that vFzg >vSet +delta, transition 311 occurs,whereupon “resume-delay” mode 305 is assumed by preventing a brakingmeasure. If vehicle speed vFzg is reduced below vSet+delta, the“resume-delay” mode is canceled and the vehicle is continued in normalregulating mode. The second possible mode that can be assumed fromnormal operating mode 303 is “suspend” mode 306. If, in normal operatingmode 303, the gas pedal is operated in the sense of increasing thespeed, the regulating operation is interrupted and vehicle speed vFzg isincreased to a value greater than vset+delta, so transition 313 leadsinto “suspend” mode 306. If the driver subsequently lets off the gaspedal while the speed is still elevated, thus fulfilling transitioncondition 314, “suspend” mode 306 develops into “suspend-delay” mode307. Subsequently, the vehicle speed declines again slowly until meetingtransition condition 315, which presupposes vFzg <vSet+delta. In thiscase, the “suspend-delay” mode which prevents braking goes back tonormal operating case 303 where a braking measure is provided.

[0024] Operating modes 305 and 307 are the two modes which are alsoreferred to as second operating modes. In these two modes, a brakingmeasure is prevented to simulate the driving response of a human driverand thus prevent unexpected regulating responses by the cruise controlsystem. When downhill driving is detected in these two modes 305 and307, braking is nevertheless performed to prevent acceleration of thevehicle due to negative road resistance.

[0025] These two special cases of the “resume” operating mode and the“suspend” operating mode are thus handled in a uniform manner.

[0026] A driving response that corresponds to that of a human driver andthus seems logical and reproducible to the driver has thus beendeveloped through the method according to the present invention. Thecruise control system can therefore be operated with an optimallyadapted operating mode in all situations, so the driver and the roadusers following the driver are not exposed to any unnecessary dangers.

What is claimed is:
 1. A method of setting the longitudinal speed of avehicle to a setpoint speed of a vehicle, in particular on the basis ofa regulation, having controllable brake units, wherein in the case of atleast one first operating mode (normal deceleration case) in which thelongitudinal speed of the vehicle exceeds the setpoint speed by apreselectable extent, the setpoint speed is set by controlling the brakeunits, and in the case of at least one second operating mode(resume-delay, suspend-delay) in which the longitudinal speed of thevehicle exceeds the setpoint speed by the preselectable extent, thesetpoint speed is set without controlling the brake units.
 2. The methodaccording to claim 1, wherein the second operating mode is initiatedwhen the vehicle longitudinal speed exceeds the setpoint speed by thepreselectable extent, and at the same time the operating element forresumption of the speed setting (resume) is operated (resume-delayoperating mode).
 3. The method according to claim 1, wherein the secondoperating mode is initiated when the vehicle longitudinal speed exceedsthe setpoint speed at least by the preselectable extent (suspend-delayoperating mode) due to actuation of a means operable by the driver ofthe vehicle for selecting the speed, in particular a gas pedal, in thesense of a speed increase.
 4. The method according to claim 1, whereinthe second operating mode is terminated when the longitudinal speed ofthe vehicle exceeds the setpoint speed by less than the preselectableextent, or a time limit on the second operating mode is exceeded, or thedriver reduces the setpoint speed by actuating at least one operatingelement, or the driver deactivates the system for setting the speed byactuating at least one operating element for deactivation of the systemor by actuating a braking device, or a distance and speed sensorprovided on the vehicle, preferably an ACC sensor, detects an obstaclein the same lane as the vehicle, its distance being less than apreselectable distance.
 5. The method according to claim 1, wherein inthe case of the second operating mode and simultaneous detection thatthe vehicle is driving downhill, a braking measure is initiated, itsdelay moment depending on the gradient of the downhill segment of road,in particular when the negative road resistance is greater than the dragon the vehicle engine.
 6. The method according to claim 1, wherein theoccurrence of the second operating mode is flagged by setting ordeleting identifiers in a respective device, different identifiers beingprovided for the “resume-delay” case or the “suspend-delay” case, sothat a distinction can be made between these two cases.
 7. A device forregulating the longitudinal speed of a vehicle and the distance of avehicle from a second vehicle driving in front of it, in which case thisdevice may have one or more of the following features: means forcontrolling braking devices, a predetermined first identifier whichindicates the presence of at least one preselectable first operatingmode (normal deceleration case) in which the longitudinal speed of thevehicle exceeds the setpoint speed by a preselectable extent, and thesetpoint speed is set by controlling the brake units, a predeterminedsecond identifier which indicates the presence of at least onepreselectable second operating mode (resume-delay, suspend-delay) inwhich the longitudinal speed of the vehicle exceeds the setpoint speedby the preselectable extent, and the setpoint speed is set withoutcontrolling the brake units, means for detecting and processing aninclination of the road surface in the longitudinal direction of thevehicle, driver operable means for activation, deactivation, resumptionand adjustment of the setpoint speed of the system for setting thespeed.
 8. The device according to claim 7, wherein the occurrence of thesecond operating mode is detected and it is noted in the device when thelongitudinal speed of the vehicle exceeds the setpoint speed by thepreselectable extent and at the same time the operating element forreactivation of the speed setting (resume) is actuated (resume-delayoperating mode) or when the longitudinal speed of the vehicle exceedsthe setpoint speed at least by the preselectable extent (suspend-delayoperating mode) due to actuation of a means operable by the driver ofthe vehicle for selecting the speed, in particular a gas pedal, in thesense of increasing the speed.
 9. The device according to claim 7,wherein the second operating mode is terminated when the device detectsthat the longitudinal speed of the vehicle exceeds the setpoint speed byless than the preselectable extent, or a time limit on the secondoperating mode is exceeded, or the driver reduces the setpoint speed byactuating operating elements, or the driver deactivates the system forsetting the speed by actuating at least one operating element fordeactivation of the system or by actuating a braking device, or anobstacle is in the same lane as the vehicle, its distance being lessthan a preselectable distance.
 10. The device according to claim 7,wherein when the second operating mode prevails and simultaneously thesystem detects that the vehicle is driving downhill, the device performsa braking measure, its delay moment depending on the gradient of thedownhill segment of road, in particular when the negative roadresistance is greater than the drag on the vehicle engine.